Three sources familiar with the helicopter company's operations told The New York Times that Island Express Helicopters was limited by the Federal Aviation Administration (FAA) to working under visual flight rules.

Visual flight rules means that a pilot can only fly in conditions where they can see the ground, and are barred from flying solely by using their instruments, which is the norm for foggy or night conditions.

According to The Times, the pilot himself, Ara Zobayan, did have instrument certification. But even though he had that ability, he was bound by the company's certification not to rely on it.

Business Insider could not immediately reach Island Express Helicopters for comment on Thursday.

On Monday, Island Express Helicopters released a statement about the accident:

"One of our helicopters, N72EX, Sikorsky S76, was involved in an accident on Sunday, January 26th in the Calabasas area of LA County.

"We are deeply saddened by this tragedy. Our top priority is providing assistance to the families of the passengers and the pilot. We hope that you will respect their privacy at this extremely difficult time.

"The pilot, Ara Zobayan, was our chief pilot. Ara has been with the company for over 10 years and has over 8,000 flight hours.

"We are working closely with the National Transportation Safety Board (NTSB) to investigate the cause of the accident and we are grateful to the first responders and local authorities for their response to this unimaginable accident."